Field of the Invention
A technique disclosed in the specification relates to a semiconductor device and a method for producing the semiconductor device, and relates to a semiconductor device used for various power electronics and a method for producing the semiconductor device, for example.
Description of the Background Art
A semiconductor device basically has a plurality of semiconductor chips within a case that is rectangular in a plan view. The semiconductor device also has a radiating surface for exchanging heat generated by the semiconductor chips with an external radiating means. The radiating surface is insulating. The semiconductor device further has a terminal approximately facing the radiating surface and electrically connected to an external circuit.
The terminal exposed for the electrically connection to the external circuit is guided to the inside of the case as an electrode that includes a conductor. The radiating surface within the case nearby has a conductive plate that is bonded on an insulating substrate made of an insulating material such as ceramic. The conductive plate is separated in part to thus form a circuit pattern.
The semiconductor chips are bonded on the circuit pattern by a bonding means that combines electrical conduction and heat conduction. Moreover, an opposite surface of a bonding surface of each semiconductor chip is electrically connected to the circuit pattern or the electrode with bonding wires.
The circuit pattern on the substrate is made of thin conductive foil as disclosed in Japanese Patent Application Laid-Open No. 2003-243610, for example. In this case, the width of the pattern is approximately nearly half of the entire effective width of the pattern in a narrow direction (i.e., shorter-side direction) of the case in order to feed a main current through the pattern. Approximately two circuit patterns through which the main current flows are disposed in a longer-side direction of the case. Moreover, the bonding wires are strung in the narrow direction (i.e., shorter-side direction) to thus connect the semiconductor chips and the circuit pattern together. A main electrode and the circuit pattern are complicatedly connected together using gaps between the wires.
In a wire bonding apparatus, an arm that performs wire bonding has a limited length due to a mechanical strength of the arm. Furthermore, the arm is geometrically thick in a portion higher (farther) than a bonding point by a certain degree. This thick portion of the arm interferes with a portion such as a periphery of a to-be-bonded object. Hence, wire bonding within a deep and narrow case, for example, involves many restrictions. In particular, a module having a width of approximately 50 mm or less involves such restrictions conspicuously.
One method to avoid such a situation includes completing as much wire bonding as possible before fitting the case into the substrate. Unfortunately, such a method cannot be necessarily used for an electrode disposed in the case.
That is, the electrode in the case may be connected to the circuit pattern before the case is fitted into the substrate. In this case, a force is applied to a bonding portion between the electrode and the circuit pattern when the case is fitted into the substrate, to thus increase possible malfunctions. It is thus hard to choose a vulnerable bonding method such as soldering.
Meanwhile, ultra-sonic (US) bonding, when chosen, is difficult to increase a frequency due to restrictions on the shape of a bonding portion of the electrode. The US bonding, which still needs a large tool (horn), restricts the bonding within the deep and narrow case in terms of arrangement.